1. Field of the Invention
The present invention relates to a reflecting device comprising on the one hand a first trough-shaped reflector of which a median cross-section contains a main axis of propagation of an emergent waveflux from this reflector, the latter comprising a parabolic section having its focus coicident with an emissive area of a source producing said waveflux, and on the other hand a second reflector arranged inside the first reflector and downstream of said source for controlling in aperture that portion of the waveflux which is defined within a solid angle formed by two generatrices extending from the flux emitting area to outer edges of the first reflector, a plane section of the second reflector, which contains the main axis of propagation of the emitted waveflux, being formed by at least two parabolic portions of which the common focus lies in said waveflux emitting area.
2. Description of the Prior Art
It is already old in the art to concentrate the flux emitted from a source, notably a light source, to form a beam of controlled aperture, by utilizing an optical device having a parabolic or elliptic section and by disposing the source at the focus of this section.
It is also known to utilize a secondary optical device for reducing the over-all dimensions of the main optical device. However, in hitherto known structures of this last-mentioned type, i.e. comprising a main optical device and a secondary optical device, the relative position of the two devices cannot under any circumstances provide simultaneously a satisfactory convergence of the emitted flux, avoid multiple reflections and effect a maximal recovery of the emitted flux without causing the latter to be returned at least partially to its source.
Now such multiple reflections imply a considerable loss of radiating power in the form of heat, which is noxious to the optical device itself and also to source, this causing a reduction in the efficiency of the device; on the other hand, the problem of recovering the power flux is particularly acute in the case of a linear source associated with a trough-shaped reflector. In fact, in this case the aperture of the flux radiated from the source in the plane of the complete median cross-section between the two side edges of the trough is strictly equal to 360.degree., so that a relatively large amount of flux is emitted backwards. In some known reflectors this recovery of the backward flux is obtained by increasing the dimensions and therefore the cumbersomeness of the optical device, or by endeavoring to take advantage of multiple reflections, thus increasing the above-described inconveniences.